Presbyopic treatment system

ABSTRACT

A method and system for treating Presbyopia and pre-Presbyopia are provided that do not compromise the wearer&#39;s intermediate or distance vision. The system is a lens and a lens series, wherein the power profiles of the lenses are tailored to provide an amount of positive ADD power in the near vision zone that is slightly less than that which is normally required for near vision accommodation, while also providing an amount of negative spherical aberration in the peripheral optical zone. The dynamic ocular factors of the wearer&#39;s eye work in conjunction with the positive ADD power provided by the central optical zone and with the effective ADD gained from the negative spherical aberration provided by the peripheral optical zone to induce a minimally discernible amount of blur that is tuned to maximize the wearer&#39;s depth of focus.

This application is a continuation of U.S. patent application Ser. No.12/229,125, filed Aug. 20, 2008, which claims the benefits under 35 USC119(e) of U.S. Provisional Patent Application Nos. 60/957,183 filed Aug.27, 2007 and 61/125,215 filed Apr. 23, 2008, the contents of each ofwhich are herein incorporated by reference in their entireties.

TECHNICAL FILED OF THE INVENTION

The invention relates to a system for treating Presbyopia. Moreparticularly, the invention relates to a lens and a lens series that canbe worn by a person to correct, or treat, symptoms of Presbyopia.

BACKGROUND OF THE INVENTION

Presbyopia is a gradual loss of accommodation of the visual system ofthe human eye. This is due to an increase in the modulus of elasticityand growth of the crystalline lens of the eye that is located justbehind the iris and the pupil. Tiny muscles in the eye called ciliarymuscles pull and push the crystalline lens, thereby causing thecurvature of the crystalline lens to adjust. This adjustment of thecurvature of the crystalline lens results in an adjustment of the eye'sfocal power to bring objects into focus. As individuals age, thecrystalline lens of the eye becomes less flexible and elastic, and, to alesser extent, the ciliary muscles become less powerful. These changesresult in inadequate adjustment of the lens of the eye (i.e., loss ofaccommodation) for various distances, which causes objects that areclose to the eye to appear blurry.

In most people, the symptoms of Presbyopia begin to become noticeableunder normal viewing conditions at around age 40, or shortly thereafter.However, Presbyopia actually begins to occur before the symptoms becomenoticeable and increases throughout a person's lifetime. In general, aperson is deemed “symptomatic” when the residual accommodation is lessthan that required for one to read. Typical reading distance requires anaccommodation ADD of 2.0 to 3.0 Diopters. Eventually, the residualaccommodation is reduced to the point at which the individual becomes anabsolute Presbyope after age 50. Symptoms of Presbyopia result in theinability to focus on objects close at hand. As the lens hardens, it isunable to focus the rays of light that come from nearby objects. Peoplethat are symptomatic typically have difficulty reading small print, suchas that on computer display monitors, in telephone directories andnewspaper advertisements, and may need to hold reading materials atarm's length.

There are a variety of non-surgical systems that are currently used totreat Presbyopia, including bifocal spectacles, progressive (no-linebifocal) spectacles, reading spectacles, bifocal contact lenses, andmonovision contact lenses. Surgical systems include, for example,multifocal intraocular lenses (IOLs) and accommodation IOLs insertedinto the eye and vision systems altered through corneal ablationtechniques. Each of these systems has certain advantages anddisadvantages relative to the others. With bifocal spectacles, the topportion of the lens serves as the distance lens while the lower portionserves as the near vision lens. Bifocal contact lenses generally workwell for patients who have a good tear film (i.e., moist eyes), goodbinocular vision (i.e., ability to focus both eyes together), goodvisual accuity (i.e., sharpness) in each eye, and no abnormalities ordisease in the eyelids. The bifocal contact lens wearer must invest thetime required to maintain contact lenses, and generally should not beinvolved in occupations that impose high visual demands on the person.Furthermore, bifocal contact lenses may limit binocular vision. Inaddition, bifocal contact lenses are relatively expensive, in part dueto the time it takes the patient to be accurately fitted.

An alternative to spectacles and bifocal contact lenses are monovisioncontact lenses. With monovision contact lenses, one lens of the paircorrects for near vision and the other corrects for distance vision. Foran emmetropic individual, i.e., an individual who does not requiredistance vision correction, only a single contact lens is worn in oneeye to correct for near vision. With non-emmetropic individuals, one ofthe monovision contact lenses sets the focus of one eye, typically thedominate eye, at distance and the other lens adds a positive power biasto the other eye. The magnitude of the positive power bias depends onthe individual's residual accommodation and near vision requirements.Individuals with low ADD requirements typically adapt very well tomonovision contact lenses. Advantages of monovision are patientacceptability, convenience, and lower cost. Disadvantages includeheadaches and fatigue experienced by the wearer during the adjustmentperiod and decreases in visual accuity, which some people findunacceptable. As the ADD difference is increased, a loss of depthperception, night vision and intermediate vision limits itseffectiveness of monovision systems.

Simultaneous vision multifocal contact lenses are also used to treatPresbyopia. Types of multifocal contact lenses include, but are notlimited to, center distance power designs, center near power designs,annular power designs, diffractive power designs, and the like. Centernear power designs are multifocal, or progressive, contact lenses usedto treat Presbyopia. These lenses have a near vision zone in the centerof the lens that extends outwardly a distance away from the center ofthe lens and a distance vision zone that is on the periphery of the lensand is concentric with and surrounds the near vision zone. With moremodern multifocal contact lenses, known as progressive contact lenses,the transition between the near and distance vision regions is moregradual than in earlier designs. The ADD power is highest in the nearvision region of the lens and lowest or zero in the distance visionregion of the lens. In the transition region, the power continuouslydecreases from near vision ADD power to distance vision ADD power (or noADD power) as the lens transitions from the near vision zone to thedistance vision zone.

While multifocal lenses generally are effective at treating symptoms ofPresbyopia, there are many disadvantages associated with multifocallenses. Multifocal lenses designed to treat symptoms of Presbyopianormally have relatively high ADD powers in the near vision zone of thelens to provide the correction needed for near vision. The high ADDpower in the near vision zone can result in visual artifacts, or ghostimages, that affect the wearer's intermediate vision and can result inother problems that compromise the wearer's distance vision.

Another shortcoming of current Presbyopic treatment systems is that mostare ineffective at treating pre-Presbyopia, or emerging Presbyopia. Evenprior to the symptoms of Presbyopia becoming readily noticeable to aperson, that person may be experiencing pre-Presbyopia symptoms, such asinability of the vision system of the eye to accommodate in conditionsof darkness or low lighting. Progressive multifocal lenses with veryhigh near vision ADD powers are not suitable for use to treatpre-Presbyopia. CooperVision, Inc., a company headquartered in Fairport,N.Y., recently began testing a contact lens that it claims is effectiveat treating pre-Presbyopia, but insufficient information is currentlyavailable about this product to verify that the lens is actuallyeffective at treating pre-Presbyopia.

Accordingly, a need exists for a system for treating Presbyopia andpre-Presbyopia that is effective and that does not compromise thewearer's intermediate or distance vision through the stages ofPresbyopia.

SUMMARY OF THE INVENTION

The invention provides a lens and a lens series for treating Presbyopiaand pre-Presbyopia. Each lens comprises a central optical zone, aperipheral optical zone and a transition zone. The central optical zonehas a power profile that provides an ADD power ranging from a maximumADD power of between about 0 diopters and about 2.4 diopters and aminimum ADD power of between about 0 diopters and 0.2 diopters. Theperipheral optical zone has a power profile that provides an amount ofnegative spherical aberration between a semi-diameter of about 2 mm anda semi-diameter of about 3 mm. The difference between the amount ofnegative spherical aberration provided at the inner semi-diameter of theperipheral optical zone and the amount of negative spherical aberrationprovided at the outer semi-diameter of the peripheral optical zoneranges from a minimum absolute value of about 0.65 diopters and amaximum absolute value of about 1.25 diopters. The transition zone ofthe lens is interposed between and connected to the central optical zoneand the peripheral optical zone and provides a transition between thecentral optical zone and the peripheral optical zone. The transitionzone has a power profile that is continuous.

The invention provides a method for designing a lens series for treatingPresbyopia wherein each lens of the series has a power profile thatprovides the central optical zone with a selected amount of ADD powerand that provides the peripheral optical zone with a selected amount ofnegative spherical aberration. A transition zone is interposed betweenand connected to the central optical zone and the peripheral opticalzone, and provides a transition between the central optical zone and theperipheral optical zone. The power profiles for each lens are defined bythe same mathematical function, except that the dc bias terms in thefunction for each lens of the series are different.

In accordance with another embodiment, the invention provides a methodfor designing a lens for treating Presbyopia comprising selecting apower profile for a central optical zone of the lens, selecting a powerprofile for a peripheral optical zone of the lens, and selecting a powerprofile for a transition zone of the lens. The power profile of thecentral optical zone is selected to provide an ADD power ranging from amaximum ADD power of between about 0 diopters and about 2.4 diopters anda minimum ADD power of between about 0 diopters and 0.2 diopters. Theperipheral optical zone has a power profile that provides an amount ofnegative spherical aberration between a semi-diameter of about 2 mm anda semi-diameter of about 3 mm. The difference between the amount ofnegative spherical aberration provided at the inner semi-diameter of theperipheral optical zone and the amount of negative spherical aberrationprovided at the outer semi-diameter of the peripheral optical zoneranges from a minimum absolute value of about 0.65 diopters and amaximum absolute value of about 1.25 diopters. The transition zone isinterposed between and connected to the central optical zone and theperipheral optical zone and provides a transition between the centraloptical zone and the peripheral optical zone. The power profile selectedfor the transition zone is continuous.

These and other features and advantages of the invention will becomeapparent from the following description, drawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a plan view of a contact lens in accordance with anillustrative embodiment of the invention.

FIG. 2 illustrates a plot of three different power profiles thatrepresent examples of power profiles that are suitable for the lensshown in FIG. 1.

FIG. 3 illustrates a plot of three different curves that represent therates of change of the three profiles shown in FIG. 2 in diopters/mmacross the central optical zone.

FIG. 4 illustrates a plot of a portion of the power profile in theperipheral optical zone shown in FIG. 1 extending from about 2.0 mm toabout 3.0 mm from the center of the lens.

FIG. 5 illustrates a plot of a curve 81 that represents the rate ofchange of the profile shown in FIG. 4 in diopters/mm across theperipheral optical zone.

FIG. 6 illustrates two power profiles of two lenses of the same seriesthat have different dc bias terms in accordance with an embodiment ofthe invention.

FIG. 7 illustrates a flowchart that represents the method of theinvention in accordance with an illustrative embodiment for providing alens series for treating Presbyopia.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The invention relates to a treatment system for treating Presbyopia andpre-Presbyopia that does not compromise the wearer's intermediate ordistance vision. For ease of discussion, the terms “Presbyopia” and“pre-Presbyopia” will be referred to hereinafter as simply “Presbyopia”.The invention is directed to a lens series comprising lenses that aretailored to provide an amount of positive ADD power in the centraloptical zone that is tuned to the residual accommodation and thedynamics of the individual's visual system and to provide an amount ofnegative spherical aberration in the peripheral optical zone. As an eyeaccommodates for a near vergence, the pupil constricts (myosis) and thespherical aberration of the optical system becomes more negative. Thesedynamic ocular factors act to increase the depth of focus of theindividual's visual system. In essence, these dynamic ocular factorswork in conjunction with the positive ADD power provided by the centraloptical zone of the lens and with the effective ADD gained from thenegative spherical aberration provided by the peripheral optical zone ofthe lens to induce a minimally discernible amount of blur. Thecombination of all of these factors results in a minimally discernibleamount of blur that is tuned to maximize the individual's depth offocus. The manner in which these goals are achieved will now bedescribed with reference to a few illustrative embodiments of theinvention.

The lenses of the invention are described herein in terms of dioptricpower profiles. A lens series is defined herein as the range of ADDpowers for a given ADD parameter. For example, a typical spherical lensseries has ADD powers that range from −10 diopters to +6 diopters in0.25-diopter steps. An ADD parameter is the aberration or dioptric powerperturbation in the optical zone needed to increase the depth of focusby a target magnitude. The magnitude and functional form of theperturbation of a given ADD parameter is targeted for a given magnitudeof residual accommodation. Thus, a particular ADD parameter isassociated with all of the lenses in a particular lens series. MultipleADD parameters are possible, and each ADD parameter targets a particularstage of Presbyopia. All of the power profiles of a given series aredefined by the same equation, except that the dc term of the equation isdifferent for each lens of the lens series. Therefore, a particularequation having particular coefficients and mathematical operatorscorresponds to the ADD parameter, whereas the dc term in that equationcorresponds to the ADD power.

FIG. 1 illustrates a plan view of a contact lens 1 in accordance with anillustrative embodiment of the invention. For purposes of describing theprinciples and concepts of the invention, it will be assumed that acontact lens in accordance with the invention has at least a centraloptical zone 10, a peripheral optical zone 20, and a transition zone 30that bridges the central optical zone 10 to the peripheral optical zone20. For these purposes, the entire optical zone of a contact lens inaccordance with the invention will be assumed to comprise the centraloptical zone 10, the transition zone 30 and the peripheral optical zone20, although any of these zones may be made up of multiple zones.

For a typical contact lens, the entire optical zone is about 7.0 to 8.0millimeters (mm) in diameter. For the purposes of describing theprinciples and concepts of the invention, it will be assumed that thecentral optical zone ranges in diameter from about 2.0 to about 4.0 mm,and preferably is about 3.0 mm in diameter. The peripheral optical zone20 is an annulus surrounding the central optical zone 10. Outside of theperipheral optical zone 20 is an outer peripheral region 25 thatgenerally does not serve any optical purpose, but serves the purpose offitting the anterior surface of the lens 1 to the surface of the eye.The entire lens 1, including this outer peripheral region 25 istypically about 13.8 mm to about 14.60 mm in diameter.

FIG. 2 illustrates a plot of three different power profiles 40, 50 and60 that represent examples of power profiles that are suitable for thelens 1 shown in FIG. 1. The vertical axis in the plot represents opticalpower in diopters and the horizontal axis represents radius from thecenter of the lens outward in millimeters. As stated above, inaccordance with the invention, it has been determined that Presbyopiacan be effectively treated by using a lens that provides an amount ofpositive ADD power in the central optical zone that is slightly lessthan that which is normally required for near vision accommodation if aselected magnitude of negative spherical aberration is provided by theperipheral optical zone. The reason that a lens having this type ofprofile is effective at treating Presbyopia is that the selectedmagnitude of negative spherical aberration provided by the peripheraloptical zone works in conjunction with the residual accommodation of theindividual's eye to extend the eye's depth of focus, thereby improvingnear vision with minimally discernible blur for intermediate vision ordistance vision. More specifically, the dynamic ocular factors of theeye work in conjunction with the positive ADD power provided by thecentral optical zone of the lens and with the effective ADD gained fromthe negative spherical aberration provided by the peripheral opticalzone of the lens to induce a minimally discernible amount of blur thatis tuned to maximize the individual's depth of focus.

The power profiles 40, 50 and 60 each have a maximum ADD power in thecentral optical zone, i.e., at the intercepts of the curves on thevertical axis, and provide negative spherical aberration in theperipheral optical zone of the lens. In the example represented by FIG.2, the maximum ADD power in the central optical zone for profile 40 isabout 0.3 diopters, the maximum ADD power in the central optical zonefor profile 50 is about 0.9 diopters, and the maximum ADD power in thecentral optical zone for profile 60 is about 1.6 diopters. The inventionis not limited to these ADD powers. The maximum ADD power typicallyranges from about 0 diopters to about 2.4 diopters at the center of thecentral optical zone 10. The minimum ADD power typically ranges fromabout 0 diopters to about 0.2 diopters at the center of the centraloptical zone 10. The amplitudes (i.e., the dc bias component) and thefunctional forms of the ADD parameters that define the profiles aredesigned to work with individuals' residual accommodation to provide asmooth, constant visual acuity level through vergence.

As indicated above, the power profile that is selected for the wearerdepends on the dynamic ocular factors of the wearer's eye. A profilehaving a higher amplitude ADD in the central optical zone will bring thenear point closer, but will result in both reduction in intermediatevision and more visual compromise through vergence. Therefore, themaximum ADD power of the central optical zone is selected based on thedynamic ocular factors of the eye so that the selected ADD power and theeffective ADD gained from the negative spherical aberration provided bythe peripheral optical zone of the lens induce a minimally discernibleamount of blur tuned to maximize the individual's depth of focus.

The minimum ADD power in the central optical zone 10 occurs at theboundary of the central optical zone 10 and the transition zone 30. Thedistance from the lens center at which the central optical zone 10 endsand the transition zone 30 begins will vary depending on the lensdesign. As indicated above with reference to FIG. 1, the central opticalzone 10 typically has a diameter that ranges from about 2.0 to about 4.0mm and preferably is about 3.0 mm. This corresponds to a radial distancefrom the lens center, i.e., a semi-diameter, of about 1.0 mm to about2.0 mm. The minimum ADD power of the central optical zone is selectedbased on the dynamic ocular factors of the eye so that the selectedminimum ADD power and the effective ADD gained from the negativespherical aberration provided by the peripheral optical zone of the lensinduce a minimally discernible amount of blur tuned to maximize theindividual's depth of focus. Negative spherical aberration, as that termis used herein, means that light rays received through the peripheralregion of the pupil are focused behind the retina while light raysreceived through the pupil center are focused on the retina.

A lens having the profile 40 is generally intended for a peopleexperiencing symptoms of pre-Presbyopia, often referred to as emergingpresbyopes. In the central optical zone 10, the profile 40 has lower ADDpowers than the ADD powers of profiles 50 and 60. For an intermediatepresbyope, i.e., a person who has begun to experience symptoms ofPresbyopia, which typically happens at around age 40, the residualaccommodation of the eye is typically only slightly less than thatrequired to focus clearly on objects that are close to the eye. Forthese individuals, a lens having the profile 50 would be suitablebecause the ADD power is slightly greater than that provided by profile40 in the central vision zone, but still less than that which wouldtraditionally by used for these individuals. For more advancedpresbyopic individuals, a lens having profile 60 provides a higher ADDpower across then entire central optical zone than that provided byprofiles 40 and 50, but still less ADD power than that traditionallyused for lenses designed for these individuals.

FIG. 3 illustrates a plot of three different curves 41, 51 and 61 thatrepresent the rates of power change of the profiles 40, 50 and 60,respectively, shown in FIG. 2 in diopters/mm across the central opticalzone 10. The curves 41, 51 and 61 are obtained by taking the firstderivative of profiles 40, 50 and 60 from r=0 mm to r=1.5 mm. The rateof power change in the central optical zone should be appropriate forthe eyes' residual accommodation. For optimal vision, the rate of powerchange over the central optical zone should be a smoothly varyingfunction. The rate of power change in the central optical zone typicallyhas a minimum absolute value of about 0.15 diopters and a maximumabsolute value of about 0.8 diopters at a semi-diameter of about 0.5 mmfrom the center of the lens. At a semi-diameter of about 1.0 mm from thecenter of the lens, the rate of power change in the central optical zonetypically has a minimum absolute value of about 0.3 diopters and amaximum absolute value of about 2.0 diopters.

It can be seen that for profile 40, the corresponding rate of change 41is constant (i.e., linear) across the central optical zone 10. It can beseen that for profile 50, the corresponding rate of change 51 increasesin magnitude from the center of the lens out to a radius of about 1.0mm, but then is generally constant from a radius of about 1.0 mm to aradius of about 1.45 mm. It can be seen that for profile 60, thecorresponding rate of change 61 increases from the center of the lensout to a radius of about 1.0 mm, and then decreases from a radius ofabout 1.0 mm out to a radius of about 1.45 mm.

The invention is not limited to the profiles shown in FIG. 2. Differentmathematical functions and/or different ADD powers from thoserepresented by profiles 40, 50 and 60 can be used to define profilesthat achieve the goals of the invention. The mathematical functions thatare used to define the power profiles are not limited to any particulartype or class of mathematical function. Each profile may be defined by asingle mathematical function, such as a polynomial function, or it maybe defined by a piece-wise function made up of multiple mathematicalfunctions. The profiles may also be defined by other functions, such as,for example, linear functions, spline functions (e.g., cubic splines andbicubic splines), Seidel functions, Zernike functions, conic functionsand biconic functions.

For example, the curves 51 and 61 shown in FIG. 3 are discontinuous at aradius of about 1.45 mm from the center of the central optical zone 10.However, because the functions that represent the profiles 50 and 60shown in FIG. 2 are continuous and therefore differentiable in the firstderivative, the profiles 40, 50 and 60 are suitable for lens designs forPresbyopia treatment. Because the profiles need not be differentiable inthe second derivative, a wider variety of mathematical functions may beused to define the profiles, including piece-wise functions and splines.

The invention is not limited with respect to the behavior of the powerprofiles in the transition zone 30 (FIG. 1). Preferably, the profile iscontinuous over the transition zone 30 to prevent vision from beingaffected by artifacts, also commonly referred to as ghosting. Anotherway of stating that the profile is continuous over the transition zone30 is to state that the profile is differentiable in at least the firstderivative over the transition zone 30. For the higher ADD powerprofiles 50 and 60 shown in FIG. 2, the continuous changes in the ratecurves 51 and 61 shown in FIG. 3 from the center of the central opticalzone 10 almost to the transition zone 30 (1.5 mm from center) ensurethat vision is not degraded by visual artifacts or ghost images.

FIG. 4 illustrates a plot of a portion of the power profile 80 in theperipheral optical zone 20 extending from about 2.0 mm to about 4.0 mmfrom the center of the lens 1 (FIG. 1). As indicated above, the powerprofile in the peripheral optical zone 20 provides an amount of negativespherical aberration. The amount of negative spherical aberration willtypically range from about −0.1 to about −0.7 diopters at the boundaryof the peripheral optical zone 20 and the transition zone 30 to about−2.0 diopters to about −2.7 diopters at the boundary of the peripheraloptical zone 20 and the outer peripheral region 25. As indicated above,the effect of this spherical aberration is that it provides an amount ofeffective ADD that works in conjunction with the positive ADD providedby the central optical zone 10 and the ocular dynamics of the eye toinduce a minimally discernible amount of blur tuned to maximize theindividual's depth of focus.

FIG. 5 illustrates a plot of a curve 81 that represents the rate ofpower change of the profiles 40, 50 and 60 in diopters/mm across theperipheral optical zone 20. The curve 81 is obtained by taking the firstderivative of any one of the profiles 40, 50 and 60 from r=2.0 mm tor=3.0 mm, i.e., by taking the first derivative of the profile 80 shownin FIG. 4. The dashed lines 82 and 83 represent bounding functions thatrepresent the typical power ranges across the peripheral optical zone20. It can be seen from FIG. 5 that the rate of change across theperipheral optical zone 20 increases in magnitude in the direction awayfrom the center of the lens and has a magnitude of about −0.67diopters/mm at a radius of about 2 mm and a magnitude of about −1.00diopters/mm at a radius of about 3 mm. Although it cannot be seen inFIG. 5 due to the X-axis stopping at a radius of 3 mm, the rate ofchange has a magnitude of about −1.33 diopters/mm at a radius of about 4mm. Looking at the bounding functions 82 and 83, the rate of powerchange across the peripheral optical zone 20 ranges in magnitude from amagnitude of about −0.5 diopters/mm at a radius of about 2 mm to amagnitude of about −1.5 diopters/mm at a radius of about 3 mm at theboundary of the peripheral optical zone 20 and the transition zone 30 toa maximum absolute value of about 1.5 diopters at the boundary of theperipheral optical zone 20 and the outer peripheral region 25.

Since the spherical aberration of the eye is essentially independent ofrefractive error, the negative spherical aberration for a lens seriespreferably will be generally equal for all lenses of the series or willvary only by a small amount over the peripheral optical zone fordifferent lenses of the series. Providing the proper magnitude range ofnegative spherical aberration in the peripheral optical zone 20increases depth of focus by providing a visually tolerable amount ofimage blur to extend depth of focus while taking into account the pupildynamics of the visual system at vergence (myosis). As stated above,negative spherical aberration, as that term is used herein, means thatlight rays received through the peripheral region of the pupil arefocused behind the retina while light rays received through the pupilcenter are focused on the retina. Equivalently stated, the periphery ofthe pupil has less power than the center of the pupil.

Defining the spherical aberration (SA) as the absolute value of thedifference in negative spherical aberration between a 2 mm semi-diameterzone and a 3 mm semi-diameter zone, as shown in FIG. 5, then thepreferred ranges of SA values are:

-   -   SA(min)=0.65 diopters    -   SA(max)=1.25 diopters    -   SA(nominal)=0.85 diopters

Preferably, for all ADD parameters, spherical aberration in theperipheral optical zone will be equal. For toric multifocal lenses, theabove ranges are valid along the Sphere meridians. The peripheraloptical zone 20 may be described by Zernike polynomials, aspheric terms,or the equivalent. The power profile in the peripheral optical zone 20may be described by a quadratic or a perturbed quadratic power function.

As stated above, for a given lens series, preferably each lens will havea power profile defined the same ADD parameter, but the dc bias termwill be different for each lens of the series. FIG. 6 illustrates twopower profiles 90 and 91 of two lenses of the same series that havedifferent dc bias terms in accordance with an embodiment of theinvention. Thus, the mathematical functions that define the profiles 90and 91 are identical except for the dc bias terms. The dc bias termcorresponds to the location at which the profile intersects the Y-axis.This value is obtained by setting all of the X-axis terms of thefunction equal to zero such that the value of the function correspondsto the dc bias term, i.e., the constant in the equation.

In accordance with another embodiment of the invention, it has beendetermined that over-plusing the near eye by a small magnitude willsometimes result in an improvement in the treatment of Presbyopia. Incases where the distance eye is the dominant eye or has the least amountof astigmatism, over-plusing the near eye by a small amount increasesdepth of focus. The term “over-plusing” as that term is used herein,means fitting an eye with a lens having a profile defined by the sameADD parameter as another lens of the series used for the other eye, butthat also has a greater dc bias term than the other lens of the series.For example, with reference to FIG. 6, the near eye would be fitted witha lens having profile 91 whereas the distance eye would be fitted with alens having the profile 90.

Although the invention has been described above with reference tocontact lenses, the invention applies equally to phakic or aphakiclenses, as well as to optical power profiles created by performingcorneal ablation. In addition, although the invention has been describedwith reference to the simultaneous vision lens shown in FIG. 1, lensesin accordance with the invention may also be used for modifiedmonovision since the power profiles described herein reduce thedisparity between distance and near powers.

FIG. 7 illustrates a flowchart that represents the method of theinvention in accordance with an illustrative embodiment for providing alens series for treating Presbyopia. A lens series is provided such thateach lens of the series has a power profile that provides ADD power inthe central optical zone and negative spherical aberration in theperipheral optical zone, as indicated by block 101. The maximum ADDpower preferably occurs at the center of the central optical zone 10(FIG. 1) and the minimum ADD power preferably occurs at the boundarybetween the central optical zone 10 and the transition zone 30. For eachlens of the lens series, the respective power profile is provided withdifferent dc bias term, as indicated by block 102. Each lens of the lensseries has a power profile in the transition region that preferably iscontinuous, as indicated by block 103, which means that the profile inthe transition region is differentiable in at least the firstderivative, but not necessarily in the second or higher derivatives.

It should be noted that the invention has been described with referenceto a few preferred and illustrative embodiments and that the inventionis not limited to these embodiments. Persons skilled in the art willunderstand that modifications can be made to the embodiments describedherein and that all such modifications are within the scope of theinvention. For example, persons skilled in the art will understand, inview of the description provided herein, that the invention is notlimited to a lens having one of the power profiles described above withreference to FIG. 2. As indicated above a variety of mathematicalfunctions and ADD parameters may be used to described power profilesthat meet the objectives of the invention of treating Presbyopia withoutsacrificing intermediate and/or distance vision. Also, although themethod described above with reference to FIG. 6 indicates separateprocesses for selecting the power profiles for the central optical zone,the peripheral optical zone and the transition zone, this may beaccomplished in a single process during which a single power profile isselected that meets all of the requirements for each of these zones.

What is claimed is:
 1. A lens for treating Presbyopia comprising: acentral optical zone having a power profile that provides an ADD powerranging from a maximum ADD power of between about 0 diopters and about2.4 diopters and a minimum ADD power of between about 0 diopters and 0.2diopters; a peripheral optical zone having an inner semi-diameter ofabout 2 millimeters (mm) and an outer semi-diameter of about 3 mm, theperipheral optical zone having a power profile that provides an amountof negative spherical aberration, a difference between the amount ofnegative spherical aberration provided by the power profile at the innersemi-diameter and the amount of negative spherical aberration providedby the power profile at the outer semi-diameter ranging from a minimumabsolute value of about 0.65 diopters and a maximum absolute value ofabout 1.25 diopters; and a transition zone interposed between andconnected to the central optical zone and the peripheral optical zone,the transition zone providing a transition between the central opticalzone and the peripheral optical zone, the transition zone having a powerprofile that is continuous.
 2. The lens of claim 1, wherein saiddifference between the amount of negative spherical aberration providedby the power profile at the inner semi-diameter and the amount ofnegative spherical aberration provided by the power profile at the outersemi-diameter has an absolute value of about 0.85 diopters.
 3. The lensof claim 1, wherein the power profile of the central optical zone iscontinuous.
 4. The lens of claim 3, wherein the power profile of theperipheral optical zone is continuous.
 5. The lens of claim 1, whereinthe maximum ADD power provided by the power profile of the centraloptical zone is about 1.6 diopters.
 6. The lens of claim 1, wherein themaximum ADD power provided by the power profile of the central opticalzone is about 0.9 diopters.
 7. The lens of claim 1, wherein the maximumADD power provided by the power profile of the central optical zone isabout 0.3 diopters.
 8. The lens of claim 1, wherein a rate of powerchange in the central optical zone is discontinuous at theinterconnection of the central optical zone and the transition zone. 9.The lens of claim 1, wherein a rate of power change in the peripheraloptical zone is continuous.
 10. The lens of claim 9, wherein a rate ofchange in the central optical zone is substantially constant.
 11. Thelens of claim 1, wherein the lens is a toric multifocal lens.
 12. A lensseries comprising lenses for treating Presbyopia, each lens of theseries comprising: a central optical zone having a power profile thatprovides a selected amount of ADD power; a peripheral optical zonehaving a power profile that provides a selected amount of negativespherical aberration; a transition zone interposed between and connectedto the central optical zone and the peripheral optical zone, thetransition zone providing a transition between the central optical zoneand the peripheral optical zone; and wherein each lens of the series hasa power profile that is defined by a mathematical function, each of themathematical functions being identical except that the dc bias terms foreach lens of the series are different.
 13. The lens series of claim 12,wherein the power profile has a rate of power change in the centraloptical zone that is discontinuous at the interconnection of the centraloptical zone and the transition zone.
 14. The lens series of claim 12,wherein the power profile has a rate of power change in the peripheraloptical zone that is continuous between a semi-diameter of about 2millimeters (mm) from a center of the lens and a semi-diameter of about3 mm from the center of the lens.
 15. The lens series of claim 12,wherein the power profile has a rate of power change in the peripheraloptical zone that has an absolute value that ranges from about 0.50diopters to about 1.00 diopters at a distance of about 2.0 millimeters(mm) from a center of the lens and has an absolute value that rangesfrom about 0.75 diopters to about 1.50 diopters at a distance of about3.0 mm from the center of the lens.
 16. The lens series of claim 15,wherein the power profile has a rate of power change in the peripheraloptical zone that has an absolute value of about 0.65 diopters at adistance of about 2.0 mm from the center of the lens and that has anabsolute value of about 1.00 diopters at a distance of about 3.0 mm fromthe center of the lens.
 17. The lens series of claim 12, wherein thepower profile has a rate of power change in the central optical zonethat has an absolute value that ranges from about 0.15 diopters to about0.8 diopters at a distance of about 0.5 millimeters (mm) from a centerof the lens and has an absolute value that ranges from about 0.3diopters to about 2.0 diopters at a distance of about 1.0 mm from thecenter of the lens.
 18. The lens series of claim 12, wherein thetransition zone has a power profile that is continuous.